The present invention relates to piston type, fluid powered motors, especially pneumatically powered motors that have a reversing valve mechanism for reversibly supplying pneumatic fluid to the piston, and more particularly to a safety mechanism associated with the reversing valve for stopping the motor when its reciprocation rate exceeds a predetermined maximum.
Pneumatically powered motors are used for a variety of prime moving tasks, for example, for powering a pump for pumping viscous resin mixtures from a reservoir or holding tank to a mold where the resin is polymerized to form a desired article. Such pneumatically powered motors are normally of the piston and cylinder type employing a pneumatic fluid such as pressurized air to reciprocate the piston, which is coupled to the resin pump. These motors normally incorporate a valve mechanism for reversing the flow of pneumatic fluid to the cylinder from one side of the piston to the other, while exhausting fluid from the cylinder on the opposite side of the piston. When the pump or other apparatus to which the drive piston is connected is under a load, for example when the pump is pumping a resin, the piston will reciprocate at a predetermined rate dependent upon, among other parameters, the pressure of the pneumatic fluid and the viscosity of the material being pumped. If however, the fluid pressure driving the piston should accidentally be increased or if the load is removed from the pump, the piston reciprocation rate will increase dramatically. Although such pumps and their associated piston type motors are generally built to withstand very high reciprocation rates and the concomitant vibration, the very high reciprocation rate can create an apprehension in the operator that the motor may catastrophically disintegrate.
In any event, the motor must be slowed down or stopped before it runs at a high reciprocation rate for a long period of time to prevent undue wear on the motor and pump components, to relieve the operator's apprehension of harm, and to allow time to replenish the supply of fluid in the pump reservoir. Prior art techniques for shutting down the motor have ranged from simply manually closing the pneumatic fluid supply line to the motor to an automatic shut-off valve in the fluid supply line that is responsive to high fluid flow accompanying high reciprocation rates. Manually blocking the supply of pneumatic fluid to the pneumatically powered motor has been a satisfactory solution but requires time to effect, during which the motor continues to reciprocate at an excessive rate, normally requires extra valve controls, increasing the expense, and normally requires such controls to be placed near the motor, potentially increasing an operator's apprehension of harm when he must shut down the motor. Interposing a flow responsive automatic shut-off valve in the pneumatic supply line has also been a satisfactory solution in the past. However, flow responsive shut-off valves are expensive, require constant adjustment, and are very sensitive to foreign matter present in the pneumatic fluid.
Accordingly, it is a broad object of the present invention to provide a mechanism associated with the pneumatic fluid supply system for a piston type motor to shut down the pneumatic motor when its reciprocation rate exceeds a predetermined maximum. More specific objects of the present invention are to provide a mechanism that does not require manual intervention to initiate the shut down process when the motor reciprocation rate reaches or exceeds a predetermined maximum; to provide a mechanism that will operate under all high reciprocation rate conditions; to provide a mechanism that will operate almost immediately upon occurrence of excessive motor reciprocation rate; to provide a mechanism that can easily be re-set so that motor operation can be resumed as soon as possible after the cause for the high reciprocation rate has been remedied; to provide a mechanism that requires little or no additional valving or other auxiliary assemblies to achieve the foregoing objects; to provide a mechanism that can be easily integrated into existing pneumatically powered motors; and to provide a mechanism that is easily and inexpensively manufactured and that requires little, and preferably no, additional maintenance.